Commercial farming depends upon the use of seeds which have excellent germination and high resistance to soil, air, and water borne diseases. Seed coatings which contain a pesticide, fungicide, or other active ingredient and a polymer to hold the active ingredient on the seed, are commonly applied to the surface of seeds to protect the seeds from fungal infestation, pest insects, etc.
Among the polymers described in the prior art are acrylics, modified polyacrylamide, and vinyl acrylic emulsions in U.S. Pat. No. 4,272,417; acrylic resin in U.S. Pat. No. 3,113,399; an aqueous emulsion of 10 to 60 percent by weight (% by wt) of a (i) water soluble neutralized copolymer of acrylic acid (AA) or methacrylic acid (MAA) and a lower acrylate, and (ii) a crosslinked copolymer of vinyl acetate and a lower alkyl acrylate, in U.S. Pat. No. 3,598,565; and, a mixture of a carboxylated hydrophilic acrylic copolymer, a crosslinking agent for the carboxy of the copolymer, an ultra-violet light absorber, and an animal or bird repellent, in U.S. Pat. No. 4,169,902. U.S. Pat. No. 5,849,320 describes insecticidal coatings for seeds which contain one or more binders selected from polymers and copolymers of polyvinyl acetate, methyl cellulose, polyvinyl alcohol, vinylidene chloride, acrylic, cellulose, polyvinylpyrrolidone and polysaccharide and a pesticide, wherein the binder forms a matrix for the pesticide. U.S. Pat. No. 5,876,739 describes insecticidal coatings for seeds containing a binder prepared from polymers or copolymers, and filler, wherein the binder forms a matrix for the pesticide and filler resulting in a substantially non-phytotoxic seed coating.
The desirable properties of the polymer used in the coating are that the polymer: (a) adheres effectively to the seed surface while providing a smooth and uniform seed coating; (b) resists hydration at high humidity; (c) results in a flexible coating which will not be friable during bagging and planting of the seeds; (d) does not allow the generation of dust during processing of the seeds; (e) is non-flammable; (f) has some degree of glycerol or ethylene glycol solubility to permit treating seeds at sub-zero temperatures; (g) is capable of forming a relatively low viscosity solution; (h) does not generate seed aggregates during the coating process; (i) allows seed treating throughput of at least 100 bushels/hr.; (j) is permeable to both water and oxygen; and, (k) can be easily washed off processing equipment when deposited thereon during treating of the seeds with the seed coating formulation, or when planting the treated seeds.
A major concern of the seed coating process is the temperature at which the coating is applied to the seeds. For example, seeds harvested in the fall are normally coated during the winter months when temperatures are low in order to be ready for spring planting. At such low temperatures, typically less than 20.degree. C., polymers having a Tg&gt;20.degree. C. have a tendency to form discontinuous films which exhibit cracking and flaking. This problem is made worse by the rubbing action of the seeds during bagging, transportation, and handling processes, particularly when such seeds are coated at low temperatures. These seed coatings which are friable or flake off sacrifice protection of the seed and cause dust. Moreover, since many active ingredients in the seed coating compositions tend to be injurious to humans and to the environment, "dusting" of coated seeds during handling and planting is particularly to be avoided.
It would be advantageous to develop a seed coating composition which strongly adheres to seeds and provides a uniform coating on seeds that is resistant to cracking and flaking even during handling and transportation of the seeds, when the seed coating composition is applied at a temperature of less than 20.degree. C.